Abstract In New York, the achievement of 90-90-90 goals is jeopardized not by limited access to affordable care and treatment, but by persistent disparities in HIV viral suppression (VS). Complex behavioral and structural barriers to achieving and maintaining VS require coordinated, combination approaches to meet medical and social service needs. In 2009, at 28 Ryan White Part A (RWPA)-funded agencies, the New York City (NYC) Department of Health and Mental Hygiene (DOHMH) launched a multi-component HIV Care Coordination Program (CCP) directed toward the most vulnerable, high-need persons living with HIV (PLWH) in NYC. A systematic CCP effectiveness study began in 2013 (R01 MH101028; PIs: Irvine, Nash). Findings to date suggest that the CCP is superior to usual care for high-need subgroups of PLWH, but there remains substantial room for improvement in short- and long-term VS. In an immediate evidence-to- practice feedback loop, the DOHMH is implementing a refined CCP model in 2018. Greater focusing, tailoring and cues for delivery of key components are expected to increase CCP engagement, reach, fidelity, scalability, effectiveness and impact. The aims of the proposed study are to: 1) Estimate the effectiveness of the revised (vs. original) CCP on timely VS (?4 months), using experimental methods (Aim 1); 2) Estimate the effectiveness of the revised CCP (vs. `usual care') on longer-term VS, including VS at 12 months and durable viral suppression (DVS) at 24-36 months, using rigorous observational comparison group methods (Aim 2); and 3) Identify attributes and drivers of provider and client engagement in the intervention and provider and client preferences for future revised-CCP delivery and receipt (Aim 3). Prior studies have not demonstrated any intervention to be effective at improving short- and long-term VS among the many PLWH with major barriers to HIV care continuum engagement. The proposed study, to be conducted on a large scale in real-world HIV service settings, will document the rollout and effects of evidence-informed implementation course corrections to an intervention model focused on these most vulnerable PLWH. In this way, the work will advance a second generation of interventions capable of strengthening the care continuum among PLWH who have been unable to achieve desired ART outcomes in existing interventions, due to major structural or psychosocial barriers.